The invention relates to a circuit for amplifying and/or attenuating a signal, which circuit has an input terminal for receiving an input signal and an output terminal for supplying an output signal, which circuit also comprises an amplifier stage having an inverting input and a non-inverting input, an output, and a controllable negative-feedback loop from the output to the inverting input. Such a circuit is known from U.S. Pat. No. 3,908,172.
The known circuit comprises two differential amplifiers.
The negative feedback of the amplifier stage and consequently the transmission of the circuit is changed in that the current distributions in the two differential amplifiers are changed in opposite senses by varying a direct voltage. The known circuit operates as a treble or bass control. However, the invention is not limited to circuits operating as treble or bass control circuits but also applies to circuits operating as frequency-independent volume control circuits. The known circuit has a number of disadvantages. If the quiescent current in the differential amplifiers is low, the circuit exhibits a high noise level. If the quiescent current is increased, the noise contribution is reduced but then the circuit exhibits substantial distortion.